Rapid spread of knockdown resistance allele frequencies in a suburban population of Aedes albopictus

Aedes albopictus is a major vector of arboviral diseases and is often targeted by pyrethroid-based mosquito control in residential areas. While knockdown resistance (kdr) mutations are well documented in Ae. aegypti, their emergence in Ae. albopictus has been less studied, particularly in suburban environments where insecticide application is often uncoordinated. Understanding the temporal and spatial dynamics of resistance evolution in this context is critical for preserving the effectiveness of public health interventions. We conducted longitudinal sampling of Ae. albopictus populations in Wake County, North Carolina, from 2016 to 2024. Using a novel allele-specific PCR melt curve assay, we genotyped 2,273 mosquitoes at the F1534S locus in the voltage-gated sodium channel gene. Resistance allele frequencies were calculated annually and mapped across the county for three key years--2016, 2018, and 2023-- representing the pre-emergence, initial detection, and widespread phases of resistance development. Selection and dominance were estimated using the Wright-Fisher Approximate Bayesian Computation algorithm for locus F1534S. The F1534S resistance allele was first detected in 2018 at a central, affluent neighborhood. By 2023, the allele had spread throughout the sampling region, with the highest frequencies near the site of first detection. Resistance allele frequency peaked at 0.36 in 2023, accompanied by an increase in heterozygous and homozygous resistance genotypes. Temporally sampled sites showed consistent trends in rising resistance, with all temporally-sampled locations harboring resistance genotypes by 2022. The resistance allele was found to be under high selection pressure and partially recessive in this population. Our findings reveal rapid emergence and spatial expansion of the F1534S kdr allele in Ae. albopictus populations in a suburban setting. The pattern of spread suggests strong local selection pressure, likely driven by residential pyrethroid use. These results highlight the need for proactive resistance monitoring and integrated management strategies that address private-sector contributions to insecticide selection pressure.